Timber durability and treatments

Approx read time: 2 minutes

Are you choosing the right timber for your project based on its durability and treatment?

Often when selecting a timber for a job, the price is a factor for your customer. But if you base it solely on price, it may not necessarily be fit for purpose for your specific job if you don’t consider the durability of the timber and the exposure hazard level of the situation.

The more durable timbers, like a hardwood species such as ironbark, are often at the pointy end of the price range, due to their suitability for a variety of conditions that require a higher durability. The price variance could be due to a number of factors like demand/supply pressures or additional supply processing costs. Sometimes cheaper timbers can be a durable option when they have the appropriate treatment.

The most common wood preservative treatments that you will see through NHS are:

  • Chromated Copper Arsenate (CCA)
    CCA has been the main type of treatment for many years. The durability of this product is attractive but should be noted that in Australia it can’t be used in high contact with children, e.g. play equipment or residential decking. (see apvma.gov.au/node/11751 for a more detailed listing). So generally you will find these in sleepers and logs at NHS and occasionally in larger end sections of treated pine due to availability issues.
  • Alkaline copper quaternary (ACQ) 
    ACQ is an arsenic-free treatment and like CCA provides protection similar to CCA. The popular treated pine commodity decking is ACQ treated.
  • Light Organic Solvent Preservatives (LOSP)
    One of the newer technologies, LOSP has some advantages in the drying aspect, which means a faster turnaround into a building yard like ourselves. This treatment type can be found in the structural timbers and primed timbers.

In addition to treatments, you should also note the hazard level which defines the exposure suitable for the application. The most common hazard classes locally are:

Hazard ClassExposureService ConditionHazardExample uses
H1Inside above groundCompletely protected from the weather, well ventilated and protected from termitesBorersSusceptible framing, flooring,
furniture, interior joinery used across Australia
H2Inside above groundProtected from wetting, no leaching.Borers and termitesFraming, flooring, furniture, interior joinery used across Australia
H3Outside above groundPeriodic moderate wetting and leachingModerate decay, borers and termitesWeatherboards, fascias, pergolas, framing etc.
H4Outside ingroundSevere wetting and leaching noncritical applicationsSevere decay, borers and termitesFence posts, retaining wall less than 1 m high, landscaping timbers.
H5Outside inground with or in fresh waterExtreme wetting and leaching, critical applicationVery severe decay, borers and termitesPiling, house stumps, power poles cooling tower fill, building poles, retaining walls more than 1m high
H6Marine watersProlonged immersion in sea waterDecay and marine wood borersBoat hulls, marine piles, jetty cross bracing, jetty landing steps

Follow all requirements for safe handling and remember treated timbers should not be burnt or used as sawdust around your pets. We have a range of safety equipment available to help you with your job.

You can refer to http://www.tpaa.com.au/timber-treatment/ for more information on specific timber treatments.

As always, come in and chat to one of our friendly team members who can discuss the right timber for your project! Contact us